Riding mowers are well known for cutting relatively wide swaths of grass in a single pass of the mower. Such mowers typically carry a plurality of individual cutting units disposed in a gang configuration in which the cutting units are staggered relative to one another. Any uncut strips of grass that would be left or are left by the cutting units in a given row are overlapped and cut by the cutting units in a preceding or trailing row. In one type of gang riding mower, the cutting units are reel cutting units having cutting reels that rotate about horizontal axes to push uncut grass against bedknives to cut the grass in a shearing action. In another type of gang riding mower, the cutting units are rotary cutting decks having one or more blades that rotate in horizontal planes about vertical axes to cut the grass by impact with sharpened cutting edges on the blades.
The cutting units in gang mowers are typically attached to the frame of the mower by suspensions that perform two functions. The suspension has a first portion that lifts and lowers the cutting units into and out of contact with the ground. This first suspension portion allows the cutting units to be lifted above the ground in a transport mode of operation or to be lowered into contact with the ground in a cutting mode of operation. The first suspension portion further allows the operator to lift the cutting units above the ground at the end of a cutting pass, to turn the mower around with the cutting units held above the ground during the turnaround, and to then lower the cutting units back into contact with the ground at the beginning of the next cutting pass. A second portion of the suspension provides the cutting units with a ground contour following ability that permits each cutting unit to adjust itself to the ground contours that it encounters in the cutting mode of operation.
When gang mowers are used to cut grass, it has been observed in the past that the cutting units sometimes exhibit a harmonic up and down vertical motion, which shall be referred to as a bobbing motion, as the mower is moving forwardly to cut grass. This bobbing motion is most often observed on reel cutting units, but rotary cutting decks are not immune to this problem. Such a bobbing motion can decrease the quality of cut as the grass height can vary slightly within the cut swath due to the bobbing motion of the cutting units. This height variation is particularly unacceptable in reel cutting units which are designed to cut grass more precisely than rotary cutting decks and at generally lower heights of cut than rotary cutting decks.
The Toro Company, the assignee of this invention, has in the past addressed this problem by adding tuned mass dampers to reel cutting units to decrease the magnitude of such bobbing motion. U.S. Pat. No. 7,669,397 is owned by The Toro Company and relates to using tuned mass dampers within the ground engaging rollers of a reel cutting unit. While this is effective in decreasing the amplitude of the bobbing motion, the amount of the decrease is limited by the relatively small size of the mass damper that can be packaged within the roller of a reel cutting unit. In addition, U.S. Pat. No. 7,934,364 is also owned by The Toro Company and relates to tuned mass dampers that are attached to the frame of the reel cutting unit. However, the size of such mass dampers and where such mass dampers can be placed on the frame of the reel cutting unit are also similarly constrained due to operational clearance that must be maintained between the reel cutting units and their respective suspensions.